echar de menos

to miss; to feel the absence of

“Te echaré de menos.” — I'll miss you.

Originally an archaic and dialectal Old Galician-Portuguese idiom, achar (de) menos (“to feel an absence”, literally “to find missing”), entering in Spanish as echar (de) menos (mistaking Old Galician-Portuguese achar (“to find”) (Spanish hallar), with echar (“to throw”), both verbs pronounced similarly and both of them with a multitude of idioms).